This invention relates to a hydraulic brake booster wherein a hydraulic input signal derived from a manual input force applied by an operator to a brake pedal is communicated to activate a control valve to supply regulated pressurized fluid to a power piston and develop operational pressurized fluid to effect a brake application as a function of the input force.
The present invention is of a type hydraulic brake boosters referred to as a xe2x80x9cfull-powerxe2x80x9d brake booster, of which the following U.S. Patents may be are considered to be typical: U.S. Pat. No. 4,441,319; 4,490,977; 4,514,981; 4,665,701; 4,685,297; 4,704,867; 4,724,674; 5,526,731 and 5,927,074. In such brake boosters, an accumulator is charged with fluid pressure and selective activated through movement of a control valve by an input member to present pressurized fluid to an actuation chamber that acts on an actuation piston. The actuation piston in turn provides a force for moving pistons of a master cylinder to pressurize operational fluid that is presented to wheel brakes to effect a brake application. The operational pressure that is developed is proportional to the force applied to the actuation piston and inversely proportional to the cross-sectional area of the piston in the master cylinder for a given force applied to an input member by an operator to move the control valve. The resulting travel of the input member and brake pedal is proportional to the travel of the actuation piston in the master cylinder. This type of hydraulic brake booster functions in a satisfactory manner, however during a manual application, the input force applied to move the pistons in the master cylinder is communicated through control and as a result some lost travel is experienced in the development operational pressure to effect a brake application. A reduction in the loss travel can be achieved by the structure disclosed in co-pending patent U.S. patent application Ser. No. 10/061,648 filed Jan. 31, 2002, however, such structure while functioning in a desired manner is very compact.
In the present invention a hydraulic brake booster has a housing with a piston arrangement located in a power bore that is connected to a control valve located in a separate control bore such that an input force applied to the piston arrangement is hydraulically communicated to activated the control valve to communicate regulated pressurized supply fluid to the power bore that acts on the piston arrangement to develop pressurized operational fluid in effecting a brake application.
In accordance with this invention, the housing of the hydraulic brake booster has a first stepped bore is connected to a first set of wheel brakes in a vehicle while the control bore is connected to a source of pressurized supply fluid, the first stepped bore and a second set of wheel brakes of a vehicle. An input force applied to the piston arrangement through an input member connected is hydraulically communicated as an input signal to activate the control valve and communicate the regulated pressurized supply fluid from the control bore to the first stepped bore and directly to the second set of wheel brakes during a brake application. The regulated pressurized supply fluid as received by the first stepped bore acts on and moves the piston arrangement in the first stepped bore to pressurize operational fluid therein that is supplied to first set of wheel brakes during a brake application. The hydraulic brake booster is characterized in that the piston arrangement has a cylindrical member with a first peripheral surface concentrically located in the first stepped bore to define an output chamber, a relief chamber and an power chamber within the housing. In turn, the cylindrical member has a second stepped bore therein for receiving a reaction piston that has a second peripheral surface concentrically located in the second stepped bore while the reaction piston has an axial bore therein for receiving a plunger to define an actuation chamber therein. The plunger is directly connected to input member and resiliently linked with a poppet valve located in the axial bore for controlling communication of fluid between the actuation chamber, the relief chamber and the control bore. When an input force is applied by an operator, the input member initially moves the plunger and poppet valve to interrupt hydraulic communication from the actuation chamber to the relief chamber and thereafter moves the plunger to pressurize fluid in the actuation chamber and create a correspondingly hydraulic input signal. This hydraulic input signal activates the control valve in the control bore such that regulated pressurized supply fluid is supplied to the power chamber for moving the first cylindrical body toward the output chamber and pressurize fluid in the output chamber to a predetermined level that the operational fluid is supplied to the first wheel brakes during a brake application that is proportionally to the input force. The control valve is characterized by an actuation piston having a first effective area for receiving the hydraulic input signal during brake application and in a second embodiment by second and third effective areas for receiving second and third hydraulic inputs under the control of an Electronic Control Unit (ECU). The second and third hydraulic inputs are derived by the ECU from sensed conditions relating to the operation of a vehicle and may modify the input signal during a brake application or under certain conditions independently activate the control valve to effect a brake application to eliminate or at least reduce the effect of the sensed conditions.
An advantage of this invention resides in a hydraulic brake booster wherein a first set of wheel brakes is supplied with operational fluid pressure created from regulated pressurized supply fluid and a second set of wheel brakes is directly supplied with regulated pressurized supply fluid to effect a brake application.
An object of this invention is to provide a hydraulic brake booster with a control valve that is hydraulically operated as a function of an input force applied to a plunger by an operator to proportionally develop an output force that acts on a piston arrangement to pressurize operational fluid that is supplied to wheel brakes to effect a brake application.
A further object of this invention resides in a brake system having a control valve with an actuation piston having a plurality of effective areas that may receive hydraulic inputs under the control of an ECU to modify an operational hydraulic input signal derived from an input force applied by an operator to effect a brake application.